Pope Francis has taken an unequivocal stand against legalisation as a means to fight drug addiction and criticised the trend in Latin America to decriminalise narcotics.
In his first public address on the issue, the new pontiff said during visit to a Rio de Janeiro hospital run by Franciscan monks that education was the way to end drug use.
"A reduction in the spread and influence of drug addiction will not be achieved by a liberalisation of drug use, as is currently being proposed in various parts of Latin America," Pope Francis said.
Some prominent Latin American leaders are moving towards support for the decriminalisation of drugs after decades of violence generated by the unsuccessful war on drug trafficking cartels in the region.
Thousands of well-wishers lined the streets in the rain to see Francis arrive at the hospital where he opened a wing that will treat alcoholics and drugs addicts.
The pope received another rapturous welcome earlier in the day at the country's main religious shrine where he urged young people to shun the "ephemeral idols" of money and pleasure and cherish traditional values to help build a better world.
On the third day of his week-long visit for World Youth Day, a biennial Church gathering being celebrated in Rio, Francis landed by helicopter in Aparecida, a shrine of the Virgin Mary that is venerated as the patroness of Brazil, home to the biggest Roman Catholic population in the world.
The shrine 260km west of Rio is also the site where Francis, then a cardinal in Argentina, cemented his place as a leader of the Church during a 2007 conference attended by Pope Benedict XVI.
The World Youth Day events, which are expected to attract more than 1 million people from around the world, are an effort by the Vatican to galvanize young Catholics at a time when rival denominations, secularism and distaste over sexual and financial scandals continue to lead some faithful to abandon the Church.
Security around the pope appeared much more organised than upon his Monday arrival in Rio, where adoring crowds at one point surrounded his car.
In Aparecida, where tens of thousands gathered for the pope's first public mass of the visit, Francis rode in a white popemobile with open sides and a transparent top. Security squads kept the vehicle safely within barriers behind which tens of thousands of ecstatic faithful cheered, sang and waved flags.
The pope's desire to remain simple and close to his flock has complicated security around his visit, especially after he used a modest Fiat hatchback for his ride into Rio from the airport.
Vatican spokesman Father Federico Lombardi said Vatican and Brazilian officials held what he called "a routine meeting" to discuss how the trip was going and made one change - that Francis would ride in a closed car from Rio airport to the hospital on his return from Aparecida.
"Benedict was holy, an intellectual, rational man. But Francis is familiar, close. We feel like he is one of us. He's like the pope next door," said Friar Leonardo Pintu, standing in the rain outside the hospital.